This invention relates to an inspection method and inspection apparatus wherein a board that has been conveyed to the inspection position is photographed with a line sensor camera and inspected.
When electronic components are mounted to printed circuit boards, various kinds of inspections are performed. These include inspections of print conditions after solder printing, inspections of mounting conditions of mounted components, and inspections of conditions of components and solder after the solder has hardened.
One method for performing such inspections is the method of inspecting by using a line sensor camera to photograph boards that have been conveyed to an inspection position.
A conventional inspection apparatus is shown in FIGS. 7 to 10.
As shown in FIGS. 7 and 8, the inspection apparatus is configured such that an inspection is made by causing a line sensor camera 3 to photograph a printed circuit board 1 conveyed to an inspection position, by scanning that printed circuit board 1 in a direction (direction indicated by arrow C) along the direction of board conveyance.
More specifically, the printed circuit board 1 in the inspection position is held by a pair of rails 2 being constant in breadth and constituting a pair of holding members. The line sensor camera 3 is movable in the direction of arrow C by a movement shaft 8, and photographs the surface of the printed circuit board 1 through a reflecting mirror 10.
In an inspection apparatus configured in this way, the movement shaft 8 is sometimes caused to expand and contract or the printed circuit board 1 to expand and contract due to factors such as heat.
For this reason, in the printed circuit board 1 being inspected, as shown in FIG. 9, a first correction mark 6e and a second correction mark 6f are provided on the side where the line sensor camera 3 starts reading and on the side where it ends reading, respectively, such that these correction marks 6e and 6f are positioned on a diagonal line passing through the board 1. Using the correction marks in these two places, any discrepancy in the movement shaft 8 or printed circuit board 1 described above is corrected.
In more specific terms, when the printed circuit board 1 is photographed by the line sensor camera 3, the correction marks 6e and 6f are first recognized with the line sensor camera 3 and center positions therefor are found respectively. Coordinate positions for the correction marks 6e and 6f thus obtained by the recognition with the line sensor camera 3 are defined as (xe, ye) and (xf, yf) respectively.
Here, coordinate positions for the first and second correction marks 6e and 6f have been pre-taught as (Xe, Ye) and (Xf, Yf), respectively, and distances between the first correction mark 6e and the second correction mark 6f in the X axis direction and the Y axis direction have been known, so that based on the distances and the recognition with the line sensor camera, the ratios of the distances between the first and second correction marks 6e and 6f in the X axis direction and the Y axis direction are found, respectively, as xcex3x and xcex3y, that may be expressed as;
xcex3x=|xexe2x88x92xf|/|Xexe2x88x92Xf| and xcex3y=|yexe2x88x92yf|/|Yexe2x88x92Yf|.
When the ratios in the X axis direction and the Y axis direction are both valued 1, it can be judged that there is no expansion or contraction in the movement shaft 8 or the printed circuit board 1. When the ratio is other than 1, however, it is judged that there is expansion or contraction in the movement shaft 8 and/or printed circuit board 1, whereupon adjustments are made to respective coordinate positions in an image so that the recognized positions of the correction marks become the taught values, and the position of the printed circuit board 1 is also adjusted.
More specifically, assuming that the expansion and contraction are uniform, respective X-coordinate and Y-coordinate values in the recognized image are divided by xcex3x and xcex3y to produce corrected values so that a corrected image can be presented.
However, as will be explained below, there is a problem with the inspection method described in the foregoing in that it cannot be used when the printed circuit board 1 is so large in the breadth direction of the rails 2 that it cannot be thoroughly scanned by the line censor camera.
When the printed circuit board 1 is too large as mentioned above, one possibility is to provide the printed circuit board 1 with a screw shaft that is movable in the breadth direction of the rails 2. By rotating the screw shaft, the printed circuit board 1 is moved in the breadth direction of the rails 2a while photographs are taken with the line sensor camera 3 a plural number of times.
When the printed circuit board 1 is photographed two times with the line sensor camera 3, for example, first, as shown in FIG. 10(a-1), the line sensor camera 3 is moved from a first scan start position 5c in the direction indicated by arrow E1, whereupon a first scan area 7a wherein a first inspection point 11a is provided is photographed.
Next, as shown in FIG. 10(a-2), the printed circuit board 1 is moved in the direction indicated by arrow E2 by the screw shaft, and a second scan area 7b wherein a second inspection point 11b is provided is photographed from a second scan start position 5d. 
The printed circuit board 1, after photographing is concluded, is moved in the direction indicated by arrow F by the screw shaft, as shown in FIG. 10(a-3), and returned to the original position.
When there is contained a process step for moving the printed circuit board 1 by a screw shaft in the breadth direction of the rails 2, as described above, there is a problem in that when printed circuit boards 1 are conveyed successively and each printed circuit board undergoes inspection, even if the position of the printed circuit board 1 is altered by rotating the screw shaft for the same amount each time, the resulting amount of movement will not be constant in actual practice because of the influence of the thermal expansion of the screw shaft.
FIGS. 10(b-1) to 10(b-3) show the inspection method for a case where there has been thermal expansion in the screw shaft.
FIG. 10(b-1), where photographing is done in the same manner as shown in FIG. 10(a-1), shows a reference position for moving the printed circuit board 1 with the screw shaft, so that the first scan start position 5c and the first scan start position 5e are at the same position, and there is no discrepancy between the first scan area 7a and the first scan area 7c photographed by the line sensor camera 3.
However, when thermal expansion occurs in the screw shaft, the moved printed circuit board 1, as shown in FIG. 10(b-2), even though the screw shaft is rotated for the same amount as shown in FIG. 10(a-2), exhibits a discrepancy between the second scan start position 5f and the second scan start position 5d in the breadth direction of the rails 2.
As a result, the distance from the second scan start position 5d to the second correction mark 6f as shown in FIG. 10(a-2) differs from the distance from the second scan start position 5f to the second correction mark 6h as shown in FIG. 10(b-2). Likewise, the distance from the second scan start position 5d to the second inspection point 11b as shown in FIG. 10(a-2) differs from the distance from the second scan start position 5f to the second inspection point 11d as shown in FIG. 10(b-2). Accordingly, overall dislocation has occurred between the image including the first scan area 7c and the second scan area 7d as shown in FIG. 10(b-3), and the image including the first scan area 7s and the second scan area 7b as shown in FIG. 10(a-3).
Thus, when a discrepancy in the rotational driving amount of the screw shaft occurs due to heat or the like, a discrepancy occurs in the scan start position, so that a contraction correction method that uses a first correction mark 6c and a second correction mark 6f, as described in the foregoing, cannot be employed.
An object of the present invention is to provide a high-precision inspection apparatus and inspection method capable of inspecting a large board by laterally moving the board and photographing the board for a plural number of times before and after the lateral moving.
The inspection method of the present invention is characterized in that a to-be-inspected board is moved laterally and an amount of movement of holding members of the board is corrected based on an amount of positional discrepancy of the board.
According to this aspect of the invention, large boards can be inspected, and high-precision inspections can be effected.
The inspection apparatus of the invention is characterized in that correction marks are provided on the holding members for holding the board.
According to this aspect of the invention, the inspection method of the present invention can be easily implemented.
The inspection method described in a first aspect of the present invention is a method for inspecting a to-be-inspected board by photographing the board that has been conveyed to an inspection position, in which a pair of holding members constituted of a pair of rails for holding the board are moved to move the board in a direction crossing a scanning direction of a linear sensor camera and the board that has been positioned is scanned by the photography unit along the direction of said conveyance of the board, the inspection method comprising: reading coordinate positions of correction marks applied to said holding members by said camera; computing an amount of positional discrepancy of the board by comparing coordinate positions of correction marks previously set with the coordinate position of correction marks having been read; and when there are discrepancies between said two kinds of coordinate positions, carrying out said photographing after correcting an amount of movement of the holding members based on said amount of positional discrepancy of the board.
The inspection method according to a second aspect of the present invention is a method for inspecting a to-be-inspected board by photographing the board that has been conveyed to an inspection position, in which a pair of holding members constituted of a pair of rails located in an opposed relation to each other for holding the board are moved to move the board in a direction crossing a scanning direction of a linear sensor camera and the board that has been positioned is scanned by the photography unit along the direction of said conveyance of the board, the inspection method comprising: reading a coordinate position of a first correction mark applied to one of the holding members by said camera; moving said holding members and reading a coordinate position of a second correction mark applied to the other of the holding members, said second correction mark on said the other of the holding members being on the side opposite to that of the first correction mark on said one of the holding members with the board being interposed therebetween; computing an amount of positional discrepancy of the board by comparing coordinate positions of first and second correction marks previously set with the coordinate positions of the first and second correction marks having been read; and when there are discrepancies between said two kinds of coordinate positions, carrying out said photographing after correcting an amount of movement of the holding members based on said amount of positional discrepancy of the board, wherein the first and second correction marks are provided on the side where the linear sensor camera starts reading.
The inspection method described in a third aspect of the present invention is a method for inspecting a to-be-inspected board by photographing the board that has been conveyed to an inspection position, in which a pair of holding members constituted of a pair of rails for holding the board are moved to move the board in a direction crossing a scanning direction of a linear sensor camera and the board that has been positioned is scanned by the photography unit along the direction of said conveyance of the board, the inspection method comprising: reading coordinate positions of correction mark applied to said board by said camera; computing an amount of positional discrepancy of said board by comparing coordinate positions of correction marks previously act with the coordinate positions of the correction marks having been read; and when there are discrepancies between said two kinds of coordinate positions, carrying out said photographing after correcting an amount of movement of the holding members based on said amount of positional discrepancy of the board, wherein first and second correction marks are provided on the side where the linear sensor camera starts reading, said second correction mark being provided on a diagonal line passing said first correction mark.
The inspection apparatus described in a fourth aspect of the present invention is an apparatus for inspecting a to-be-inspected board by photographing the board that has been conveyed to an inspection position, in which a pair of holding members constituted of a pair of rails for holding the board are moved to move the board in a direction crossing a scanning direction of a linear sensor camera and the board that has been positioned is scanned by the camera along the direction of said conveyance of the board, the inspection apparatus comprising: a control unit configured to read coordinate positions of correction marks applied to the holding members by the photography unit, to compute an amount of positional discrepancy of the board by comparing coordinate positions of correction marks previously set with the coordinate positions of the correction marks having been read, and when there are discrepancies between said two kinds of coordinate positions, to carry out said photographing after correcting an amount of movement of the holding members based on said amount of positional discrepancy of the board.
The inspection apparatus described in a fifth aspect of the present invention is an apparatus for inspecting a to-be-inspected board by photographing the board that has been conveyed to an inspection position, in which a pair of holding members constituted of a pair of rails for holding the board are moved to move the board in a direction crossing a scanning direction of a linear sensor camera and the board that has been positioned is scanned by the camera along the direction of said conveyance of the board, the inspection apparatus comprising: a control unit configured to read coordinate positions of correction marks applied to said board by the photography unit, to compute an amount of positional discrepancy of the board by comparing coordinate positions of correction marks previously set with the coordinate positions of the correction marks having been read, and when there are discrepancies between said two kinds of coordinate positions, to carry out the photographing after correcting an amount of movement of the holding members based on said amount of positional discrepancy of the board.